With the advent of the Internet of Things and regular data transfers between geographically-distributed data centers, metro traffic is becoming less aggregated, exhibiting more burstiness. There is a requirement to provide dynamic optical capabilities to support the bursts and reduce the level of peak provisioning. Migrating to a flexible optical physical layer in which the network can adapt in response to dynamic channel conditions and traffic requirements could hence lead to systems with tighter margins and greater resource efficiency.
Fast wavelength switching or reconfiguration is key to achieving a flexible optical network. The channel power dynamics that arise from continuously changing the input conditions of erbium doped fiber amplifiers (EDFAs) remain an unresolved obstacle. One main power dynamic effect is the amplifier transient effect, which is solved by fast amplifier control. However, after the transients there is still a power excursion that remains until the slow time scale adjustments of the wavelength selective switches (WSSs) and variable optical attenuators (VOAs) can correct the power levels. These power excursions grow in cascade and make wavelength reconfiguration a time consuming process. These power excursions occur due to EDFA automatic gain control (AGC), which maintains a constant gain by monitoring the total input and output power in the fiber, ignoring the wavelength dependent gain arising from gain ripple and tilt of the amplifier. The strict requirement that the modification of a wavelength should not impact other channels in a system becomes difficult to achieve in this dynamic network environment. Deviations from target power levels in optical networks can cause channels to exceed allocated margins for transmission, potentially resulting in sustained errors as the control mechanisms respond over long time periods and also may interact with other power control mechanisms, resulting in network instability. Degradations in the optical signal to noise ratio (OSNR) are also impacted by the EDFA gain profile and varying fiber plant characteristics. Note that OSNR and other quality of transmission (QoT) related monitoring methods introduced in the past require an established signal and thus only provide after the fact information for wavelength reconfiguration and cannot be used in the wavelength routing and assignment decisions that come before switching.